Composite negative electrode sheet, preparation method therefor, and lithium ion battery using same

Abstract

A composite negative electrode sheet, a preparation method therefor, and a lithium ion battery using same. The composite negative electrode sheet comprises a current collector (1), an active coating (2) and an insulating coating (3) which are sequentially arranged. The insulating coating (3) comprises a polymer, an inorganic filler and a fast ion conductor. The active coating (2) comprises a binder and an active material. The difference between the solubility parameters of the polymer and the binder is denoted as |△δ|, where |△δ|>0.5(J / cm3)1 / 2. The barrier property between the insulating coating (3) and the active coating (2) is effectively improved, thus improving the structural stability of the composite negative electrode sheet.

Description

A composite negative electrode sheet and its preparation method, and lithium-ion batteries using the same.

[0001] This application claims priority to Chinese Patent Application No. 2024105830892, filed on May 10, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of lithium-ion battery technology, specifically relating to a composite negative electrode sheet and its preparation method, and a lithium-ion battery using the same. Background Technology

[0003] With the rapid development of portable electronic devices, electric vehicles, and smart grids, the demand for high-performance electrochemical storage devices is increasing. Among them, lithium-ion batteries have always held a pivotal position in the commercial market due to their high energy density, high operating voltage, long cycle life, and minimal memory effect.

[0004] To meet market demands, developing lithium-ion batteries with high energy density, high cycle stability, and high safety performance has become a future development trend. A lithium battery consists of a cell made of a positive electrode, a negative electrode, and a separator. The separator separates the positive and negative electrodes, preventing electrons from freely passing through, but allowing ions in the electrolyte to freely pass between them, thus ensuring battery safety. Technical issues

[0005] Traditional battery separators are made of resin materials such as polyethylene or polypropylene. When the battery temperature is high, these separators are prone to shrinkage or melting, which can cause the positive and negative electrodes to come into direct contact, leading to short circuits and thermal runaway, and ultimately causing the battery to burn and explode, thus limiting the development of lithium-ion batteries. Technical solutions

[0006] In a first aspect, this application provides a composite negative electrode sheet, comprising a current collector, an active coating, and an insulating coating arranged sequentially. The insulating coating comprises a polymer, an inorganic filler, and a fast ion conductor. The active coating comprises a binder and an active material. The solubility parameter difference between the polymer and the binder is expressed as |Δδ|, where |Δδ| > 0.5 (J / cm³). 3 ) 1 / 2 .

[0007] Secondly, this application provides a method for preparing the above-mentioned composite negative electrode sheet, including the following operations: S1. Mixing the binder and active material evenly to obtain an active slurry, and applying the active slurry to the current collector to obtain an active coating; S2. Mixing the polymer and solvent evenly, and then adding inorganic filler and fast ion conductor to the reaction system to obtain an insulating slurry, and applying the insulating slurry to the active coating so that the insulating coating and the current collector are connected through the active coating to obtain the composite negative electrode sheet.

[0008] Thirdly, this application provides a lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode includes the aforementioned composite negative electrode sheet. Beneficial effects

[0009] The composite negative electrode provided in this application features structural stability, high ion transport efficiency, and high thermal stability. On one hand, the solubility parameter (SP) is a physical constant that measures the compatibility of materials. The polymer solubility parameter in this application is obtained by estimation using the molar attraction constants of each group or atom in the structural unit. The estimation formula is: δ=d / M·∑G i [d—density, g / cm³] 3 M—relative molecular mass of the repeating unit, g / mol; Gi—molar attraction constant of the chemical groups constituting the molecule, (J·cm⁻¹) 3 ) 1 / 2 / mol; δ—solubility parameter of the polymer, (J / cm³) 3 ) 1 / 2 The solubility parameter of the polymer is denoted by δ1, and the solubility parameter of the binder is denoted by δ2. The difference in solubility parameters between the polymer and the binder is |Δδ| = |δ1 - δ2|. By controlling the types of polymer in the binder phase of the insulating coating and binder in the active coating, so that the difference in solubility parameters between the polymer and the binder is greater than 0.5, the polymer and binder are less miscible. This effectively improves the barrier performance between the insulating coating and the active coating while maintaining a low interfacial resistance, thereby enhancing the structural stability of the composite negative electrode.

[0010] On the other hand, the insulating coating provided in this application has the advantages of electronic insulation and high ion transport efficiency. When the separator can still separate the positive and negative electrodes, by using a composite negative electrode with high lithium-ion transport efficiency, the lithium-ion insertion rate of the negative electrode can be improved, reducing the possibility of lithium ions and electrons meeting on the surface of the insulating layer and causing lithium deposition on the negative electrode. This inhibits the growth of lithium dendrites, preventing lithium dendrites from piercing the battery separator and causing internal short circuits, or even fires and explosions. When the separator is damaged or undergoes thermal shrinkage at high temperatures, the insulating coating of the composite negative electrode can effectively prevent direct contact between the conductive components of the positive and negative electrodes, preventing internal short circuits in the battery. During battery cycling, it also promotes the insertion of lithium ions into the active coating through the insulating coating, improving the charge and discharge performance of the battery and extending its cycle life.

[0011] The inorganic fillers and chemical groups on the surface of the fast ion conductors in the insulating coating exhibit strong Lewis acid-base interactions with the cations / anions in the lithium salt. These interactions can either immobilize anions or hinder anion transport, thereby jointly promoting the dissociation and ion transport of lithium salt in the electrolyte. Polar atoms in the polymer can coordinate with lithium ions dissociated from the lithium salt, enabling ion transport through chain segment coupling-decoupling, thus improving ionic conductivity and lithium-ion transport rate. In summary, by adjusting the types of materials in the insulating and active coatings, the composite negative electrode sheet can meet the above requirements, promoting lithium-ion transport and improving the safety performance of batteries using this composite negative electrode sheet.

[0012] Using the above-mentioned composite negative electrode sheet as the negative electrode, the active coating can be prepared using the binder commonly used in negative electrodes, and the lithium-ion battery using the above-mentioned composite negative electrode sheet has high thermal stability and excellent cycle performance. Attached Figure Description

[0013] Figure 1 is a schematic diagram of the negative electrode sheet provided in Embodiment 1 of this application.

[0014] Figure labels: 1 negative electrode current collector, 2 negative electrode active coating, 3 insulating coating. Embodiments of the present invention

[0015] In some implementations, |△δ|>8.5 (J / cm) 3 ) 1 / 2 .

[0016] In some embodiments, the mass ratio of the inorganic filler and fast ion conductor to the polymer in the insulating coating is 80-94:6-20. For example, the mass ratios are 94:6, 90:10, 85:15, and 80:20. By adjusting the amounts of inorganic filler, fast ion conductor, and polymer, the insulating coating can meet the above mass ratio requirements, improving the uniformity of distribution within the coating. This enhances the adhesion between the inorganic filler, fast ion conductor, and polymer, as well as the adhesion between the insulating coating and the active coating, thereby strengthening the impact resistance, structural stability, and mechanical strength of the composite negative electrode. In particular, since a gas generation mechanism exists during battery cycling, adjusting the composition of the insulating coating can make it more resistant to gas impacts and less prone to localized detachment, thus improving battery cycle stability.

[0017] In some embodiments, the solubility parameter of the polymer is represented by δ1, which is 12.7~24.9 (J / cm³). 3 ) 1 / 2 The polymers include at least one of polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene, polypropylene, polyvinyl chloride (PVC), polyoxyethylene, polymethoxyethylene glycol methacrylate (POM), polymethyl methacrylate (PMMA), polyacrylonitrile (PAB), polycarbonate, polymethyl ethylene carbonate (PMCA), PVC, and polystyrene. For example, the polymer solubility parameter δ1 is 12.7, 13.5, 14.7, 15.3, 16.1, 16.5, 17.5, 18.5, 19.2, 19.8, 20.5, 21.5, 22.5, 23.5, 24.9, etc. By comprehensively controlling the polymer solubility parameter δ1 and its type, the compatibility between the inorganic filler, fast ion conductor, and polymer in the insulating coating is improved. This enhances the electrolyte resistance and structural stability of the composite negative electrode sheet, reduces the probability of detachment or powder shedding, and provides continuous lithium-ion migration channels in the insulating coating, reducing the interfacial resistance and increasing the ionic conductivity within the composite negative electrode sheet. Furthermore, based on the solubility parameter δ1 of the polymer used, it is possible to select an active coating binder that satisfies a solubility parameter difference |Δδ| greater than 0.5.

[0018] In some embodiments, the molecular weight of the polymer is 500 to 100,000 g / mol. For example, the molecular weight of the polymer is 500 g / mol, 1000 g / mol, 5000 g / mol, 10000 g / mol, 15000 g / mol, 20000 g / mol, 25000 g / mol, 30000 g / mol, 35000 g / mol, 40000 g / mol, 45000 g / mol, 50000 g / mol, 55000 g / mol, 60000 g / mol, 65000 g / mol, 70000 g / mol, 75000 g / mol, 80000 g / mol, 85000 g / mol, 90000 g / mol, 95000 g / mol, or 100000 g / mol.

[0019] In some embodiments, the molecular weight of the polymer is 2000~80000 g / mol.

[0020] In some embodiments, the polymer includes polyvinylidene fluoride (PVDF). PVDF exhibits excellent chemical stability and corrosion resistance, effectively resisting the erosion of polar organic solvent electrolytes in lithium batteries. It also possesses good adhesion and flexibility, enhancing the structural and thermal stability of the composite negative electrode sheet.

[0021] In some embodiments, the binder for the active coating includes at least one of styrene-butadiene rubber and hydroxymethyl cellulose.

[0022] In some embodiments, the average particle size D50 of the inorganic filler is 20 nm to 3 μm, and the average particle size D50 of the fast ion conductor is 20 nm to 3 μm. For example, the average particle size D50 of the inorganic filler is 20 nm, 50 nm, 100 nm, 200 nm, 400 nm, 600 nm, 800 nm, 1 μm, 1.5 μm, 2.0 μm, 2.5 μm, or 3 μm; the average particle size D50 of the fast ion conductor is 20 nm, 50 nm, 100 nm, 200 nm, 400 nm, 600 nm, 800 nm, 1 μm, 1.5 μm, 2.0 μm, 2.5 μm, or 3 μm. By comprehensively controlling the average particle size of the inorganic filler and the fast ion conductor, the structural stability, mechanical strength, and ion migration rate of the composite negative electrode sheet can be improved. On the one hand, the use of the aforementioned inorganic fillers and fast ion conductors can improve the mechanical strength and electrolyte-accommodating volume of the composite negative electrode sheet. Simultaneously, the inorganic fillers and fast ion conductors in the insulating coating, acting as cross-linking centers, can hinder polymer chain recrystallization, thereby reducing polymer crystallinity and improving the ion transport efficiency of the insulating coating. On the other hand, when the average particle size of the inorganic fillers and fast ion conductors is within the aforementioned range, the uniformity of their distribution within the insulating coating can be improved, reducing the probability of excessively fast or slow local transport within the insulating coating. This reduces DC resistance (DCR), decreases the battery polarization rate increase, and improves battery cycle performance.

[0023] In some implementations, the ionic conductivity activation energy of the fast ion conductor is ≤0.35 eV.

[0024] In some embodiments, fast ion conductors include lithium phosphate (Li3PO4) and lithium titanate (Li4Ti5O4). 12 Lithium titanium phosphate [LiTi2(PO4)3], lithium lanthanum tantalate (Li5La3Ta2O) 12 Lithium titanium aluminum phosphate [Li] 1+x Al x Ti 2-x [(PO4)3], lithium aluminum germanium phosphate [Li 1.5 Al 0.5 Ge 1.5 [(PO4)3], Lanthanum-platinum-lithium (LLZO, Li7La3Zr2O) 12 Li 7-x La3Zr 2-x Nb x O 12 Li 7-x La3Zr 2-x Ta x O 12 ), lithium lanthanate (Li5La3Nb2O) 12 Li x La 2 / 3-xAt least one of TiO3, lithium superion conductor (LISICON), and sodium superion conductor (NASICON). According to the above proportions, using the above-mentioned fast ion conductors in combination with inorganic fillers and polymers to prepare an insulating coating not only promotes the formation of additional lithium-ion transport paths in the insulating coating and improves ionic conductivity, but also enhances the chemical stability of the composite negative electrode and the thermal stability of lithium-ion batteries using this composite negative electrode.

[0025] In some embodiments, the inorganic filler includes at least one of aluminum oxide, silicon dioxide, titanium dioxide, calcium oxide, zirconium oxide, diatomaceous earth, and kaolin.

[0026] In some embodiments, the mass ratio of inorganic filler to fast ion conductor is 1 to 9:1 to 9. For example, the mass ratio of inorganic filler to fast ion conductor is 1:9, 3:7, 5:5, 7:3, or 9:1. When the mass ratio of inorganic filler to fast ion conductor in the insulating coating falls within the above range, the insulating coating can have a higher lithium-ion transference number and higher conductivity.

[0027] In some embodiments, the porosity of the insulating coating is 30-80%. For example, the porosity of the insulating coating is 30%, 40%, 50%, 60%, 70%, or 80%. By controlling the porosity of the insulating coating, the ion transport efficiency and electronic insulation performance of the insulating coating can be improved while ensuring high mechanical strength and structural stability.

[0028] In some embodiments, the average pore size is 0.001 to 10 μm. For example, the average pore size is 0.001 μm, 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0029] In some embodiments, the thickness of the insulating coating is 0.5 to 50 μm. For example, the thickness of the insulating coating is 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm.

[0030] In some embodiments, the thickness of the active coating is 30 to 70 μm. For example, the thickness of the active coating is 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, or 70 μm.

[0031] In some embodiments, application includes at least one of coating, spraying, spin coating, dipping, dripping, and roller coating.

[0032] In some embodiments, the solvent includes N,N-dimethylacetamide.

[0033] In some embodiments, during process S2, the insulating slurry is dried to form an insulating coating. The drying temperature of the insulating slurry is 50~70°C, and the drying time is 7~9 hours.

[0034] In some implementations, the insulating coating in the composite negative electrode sheet faces the separator.

[0035] Example 1

[0036] This embodiment provides a composite negative electrode sheet, the structure of which is shown in Figure 1. The composite negative electrode sheet includes an insulating coating 3, an active coating 2, and a current collector 1 arranged sequentially. The active coating is prepared from an active slurry, and the insulating coating is prepared from an insulating slurry. The current collector is copper foil.

[0037] The insulating paste comprises polymer, inorganic filler, fast ion conductor, and solvent, with a mass ratio of fast ion conductor, inorganic filler, and polymer of 80:10:10. The inorganic filler is aluminum oxide (Al₂O₃) with an average particle size D50 of 1 μm. The fast ion conductor is lithium lanthanum oxide (Li₅La₃Nb₂O₃) with an ionic conductivity activation energy ≤0.35 eV and an average particle size of 2 μm. 12 The polymer was selected with a solubility parameter δ1 of 23.10 (J / cm³). 3 ) 1 / 2 Polyvinylidene fluoride (PVDF) with a molecular weight of 14000 g / mol was used, and acetonitrile was selected as the solvent.

[0038] The active slurry includes active materials, binders, conductive agents, and aqueous solvents. The active material is artificial graphite, and the binder has a solubility parameter δ² of 17.3 (J / cm²). 3 ) 1 / 2 The styrene-butadiene rubber (SBR) is used. Therefore, the solubility parameter difference |Δδ| between the polymer and the binder can be calculated to be greater than 0.5. Based on the mass ratio, the ratio of styrene-butadiene rubber:artificial graphite:conductive agent is 4:89:7.

[0039] The specific preparation method includes the following steps:

[0040] S1. The active material, binder, conductive agent and aqueous solvent are mixed evenly and coated on the surface of the current collector. The mixture is then dried and rolled to obtain an active coating with a thickness of 40 μm.

[0041] S2. The polymer and solvent are then mixed evenly, and inorganic filler and fast ion conductor are added sequentially to the reaction system. The mixture is stirred until homogeneous to obtain an insulating slurry. This slurry is then coated onto the surface of the active coating and vacuum dried at 60°C for 8 hours, allowing the insulating coating and current collector to connect through the active coating, thus obtaining a composite negative electrode. In the composite negative electrode, the insulating coating has a thickness of 15 μm, a pore size of 1.6 μm, and a porosity of 40%.

[0042] Example 2

[0043] This embodiment refers to the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this embodiment and Example 1 is that in the process of preparing the insulating coating, a solubility parameter δ1 of 12.7 (J / cm³) is selected. 3 ) 1 / 2 The polymer in Example 1 was replaced with polytetrafluoroethylene. The remaining raw material ratios and preparation methods were strictly consistent with those in Example 1.

[0044] Example 3

[0045] This embodiment refers to the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this embodiment and Example 1 is that in the process of preparing the insulating coating, a solubility parameter δ1 of 19.8 (J / cm³) is selected. 3 ) 1 / 2 The polymer in Example 1 was replaced with polyvinyl chloride. The remaining raw material ratios and preparation methods were strictly consistent with those in Example 1.

[0046] Example 4

[0047] This embodiment refers to the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this embodiment and Example 1 is that, in the process of preparing the insulating coating, aluminum oxide with an average particle size of 20 nm is used instead of the inorganic filler in Example 1, and lithium lanthanum oxide (Li5La3Nb2O) with an average particle size of 30 nm is used. 12 This replaces the fast ion conductor in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0048] Example 5

[0049] This embodiment refers to the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this embodiment and Example 1 is that, in the process of preparing the insulating coating, aluminum oxide with an average particle size of 3 μm D50 is used instead of the inorganic filler in Example 1, and lithium lanthanate salt Li5La3Nb2O with an average particle size of 3 μm D50 is used. 12 This replaces the fast ion conductor in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0050] Example 6

[0051] This embodiment refers to the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this embodiment and Example 1 is that in the process of preparing the insulating coating, the amount of polymer added is adjusted so that the sum of the masses of the inorganic filler and the fast ion conductor is equal to the mass of the polymer at a ratio of 75:25. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1, especially the mass ratio of the inorganic filler to the fast ion conductor.

[0052] Example 7

[0053] This embodiment refers to the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this embodiment and Example 1 is that in the process of preparing the insulating coating, the amount of polymer is adjusted so that the sum of the masses of the inorganic filler and the fast ion conductor is equal to the mass of the polymer in a ratio of 80:20. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1, especially the mass ratio of the inorganic filler to the fast ion conductor.

[0054] Example 8

[0055] This embodiment refers to the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this embodiment and Example 1 is that in the process of preparing the insulating coating, the amount of polymer added is adjusted so that the sum of the masses of the inorganic filler and the fast ion conductor is equal to the mass of the polymer in a ratio of 94:6. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1, especially the mass ratio of the inorganic filler to the fast ion conductor.

[0056] Example 9

[0057] This embodiment refers to the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this embodiment and Example 1 is that in the process of preparing the insulating coating, the amount of polymer added is adjusted so that the sum of the masses of the inorganic filler and the fast ion conductor is equal to the mass of the polymer in a ratio of 96:4. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1, especially the mass ratio of the inorganic filler to the fast ion conductor.

[0058] Comparative Example 1

[0059] This comparative example follows the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this comparative example and Example 1 is that the preparation of the insulating coating is omitted in the process of preparing the composite negative electrode sheet. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0060] Comparative Example 2

[0061] This comparative example refers to the preparation method provided in Example 1 to prepare a lithium-ion battery, which includes a positive electrode, a negative electrode, and a composite separator placed between the positive electrode and the negative electrode.

[0062] The negative electrode includes a current collector and an active coating. The active coating is made from an active slurry, and the active slurry is strictly consistent with that in Example 1.

[0063] The composite separator comprises a separator base membrane and an insulating coating. The insulating coating is made of an insulating slurry. The separator base membrane is manufactured by Enjie Company and has a thickness of 7 μm. The insulating slurry used in this comparative example is strictly consistent with that in Example 1. In the preparation of the composite separator, the preparation method provided in Example 1 is followed, with the only difference being that the insulating slurry is coated on the surface of the separator base membrane in this comparative example. Furthermore, in this comparative example, the insulating coating is composited with the negative electrode sheet, while the remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0064] A 1 mol / L LiPF6 / EC / PC electrolyte was used. The positive electrode, separator, and negative electrode were stacked in sequence, so that the insulating coating in the negative electrode was combined with the separator, and then assembled to obtain a bare cell. The bare cell was placed in an outer packaging foil, and the electrolyte prepared above was injected into the dried battery. Then, after vacuum sealing, standing, formation, and shaping processes, an 18650 cylindrical single cell was obtained.

[0065] Comparative Example 3

[0066] This comparative example refers to the preparation method provided in Example 1 to prepare a lithium-ion battery, which includes a composite positive electrode, a negative electrode, and a composite separator placed between the positive electrode and the negative electrode.

[0067] The negative electrode includes a current collector and an active coating. The active coating is made from an active slurry, and the active slurry is strictly consistent with that in Example 1.

[0068] The composite positive electrode sheet is prepared according to the method provided in Example 1, except that an insulating coating is provided on the positive electrode active coating. Furthermore, the raw material ratio of the insulating coating is strictly consistent with that in Example 1. That is, the composite positive electrode sheet in this comparative example includes a current collector, an active coating, and an insulating coating. In the preparation of the composite positive electrode sheet, the preparation method provided in Example 1 is followed, except that in this comparative example, the insulating slurry is coated on the surface of the positive electrode active coating, a ternary material is used as the positive electrode active material, and polyvinylidene fluoride (PVDF) is used as the binder in the positive electrode active coating. Moreover, the insulating coating in the composite positive electrode sheet is composite with the separator.

[0069] A 1 mol / L LiPF6 / EC / PC electrolyte was used. The separator was a membrane base film manufactured by Enjie Company. The positive electrode, separator, and negative electrode were stacked in sequence, allowing the insulating coating in the negative electrode to bond with the separator, and then assembled to obtain a bare cell. The bare cell was placed in an outer packaging foil, and the electrolyte prepared above was injected into the dried battery. After vacuum sealing, settling, formation, and shaping processes, an 18650 cylindrical single-cell battery was obtained.

[0070] Comparative Example 4

[0071] This comparative example follows the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this comparative example and Example 1 is that the solubility parameter δ1 is selected as 17.8 (J / cm³) during the preparation of the composite negative electrode sheet. 3 ) 1 / 2 Styrene-butadiene rubber was used instead of the polymer in Example 1 to make the solubility parameter difference |Δδ| between the polymer and the binder 0.5. The remaining raw material ratios and preparation methods were strictly consistent with those in Example 1, especially the mass ratio of inorganic filler to fast ion conductor.

[0072] Comparative Example 5

[0073] This comparative example follows the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this comparative example and Example 1 is that the solubility parameter δ2 is selected as 23.10 (J / cm²) during the preparation of the composite negative electrode sheet. 3 ) 1 / 2 Polyvinylidene fluoride was used instead of the binder in Example 1 to make the solubility parameter difference |Δδ| between the polymer and the binder zero. The remaining raw material ratios and preparation methods were strictly consistent with those in Example 1, especially the mass ratio of inorganic filler to fast ion conductor.

[0074] Comparative Example 6

[0075] This comparative example uses the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this comparative example and Example 1 is that, in the process of preparing the insulating coating, an equal mass of inorganic filler Al2O3 is used instead of the fast ion conductor in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1, especially the average particle size of the inorganic filler is strictly consistent with that in Example 1.

[0076] Comparative Example 7

[0077] This comparative example follows the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this comparative example and Example 1 is that, in the process of preparing the insulating coating, an equal mass of fast ion conductor lithium lanthanum oxide (Li5La3Nb2O) is selected. 12The inorganic filler in Example 1 is replaced. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1, especially the average particle size of the fast ion conductor is strictly consistent with that in Example 1.

[0078] Comparative Example 8

[0079] This comparative example refers to the preparation method provided in Example 1 to prepare a composite negative electrode sheet. The difference between this comparative example and Example 1 is that in the process of preparing the composite negative electrode sheet, the first coating and the second coating are used instead of the insulating coating in Example 1.

[0080] The difference between the first coating and the insulating coating in Example 1 is that the same mass of inorganic filler Al2O3 is used instead of the fast ion conductor in Example 1. The difference between the second coating and the insulating coating in Example 1 is that the same mass of fast ion conductor lithium lanthanum oxide Li5La3Nb2O is used. 12 The inorganic filler in Example 1 was replaced. The remaining raw material ratios and preparation methods were strictly consistent with those in Example 1, especially the average particle size of the fast ion conductor and the inorganic filler.

[0081] In other words, the composite negative electrode sheet provided in this comparative example includes a current collector, an active coating, a first coating, and a second coating arranged in sequence. The first coating includes a polymer and an inorganic filler, and the second coating includes a fast ion conductor of the polymer.

[0082] Test case

[0083] Test subjects: composite negative electrode sheets and lithium-ion batteries provided in Examples 1-9 and Comparative Examples 1-8.

[0084] Test items and test methods:

[0085] (1) Peel strength of electrode: The prepared negative electrode is cut into 30mm*200mm size and subjected to 180° tensile test to test the interface peel strength of the electrode.

[0086] (2) Battery performance test:

[0087] The composite negative electrode sheets provided in Examples 1-9, Comparative Examples 1, and Comparative Examples 4-8 were used as negative electrode sheets, and ternary materials were selected as positive electrode sheets. 1 mol / L LiPF6 / EC / PC was used as the electrolyte. The separator was a separator base membrane manufactured by Enjie Company. The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence, allowing the insulating coating in the negative electrode sheet to bond with the separator, and then assembled to obtain a bare cell. The bare cell was placed in an outer packaging foil, and the electrolyte prepared above was injected into the dried battery. After vacuum sealing, settling, formation, and molding processes, an 18650 cylindrical single-cell battery was obtained. The obtained battery and the lithium-ion batteries provided in Comparative Examples 2-3 were subjected to the following battery performance tests.

[0088] ① Thermal runaway test: This test verifies the battery's safety performance using a thermal chamber test. A thermocouple is attached to the battery surface, and the battery is placed in a thermal chamber. The battery is heated from an initial temperature (room temperature) to a higher temperature at a heating rate of 5±1℃ / min. The thermal chamber temperature is required to be 150℃, and then maintained at that temperature. The change in battery temperature over time is recorded. The time required for the battery to reach thermal runaway (the uncontrolled exothermic reaction inside the battery, causing smoke and combustion) while maintaining a constant temperature of 150℃ in the thermal chamber is determined.

[0089] ② Capacity retention rate: At 25℃, the lithium-ion battery was charged at 1C constant current and constant voltage to 4.2V, cut off at 0.05C, left to stand for 10min, discharged at 1C constant current to 2.5V, left to stand for 10min, and cycled for 400 cycles. The capacity retention rate of the battery at 1C / 400 cycles was recorded.

[0090] Test results are shown in Table 1.

[0091] Table 1. Performance results of each test subject

[0092] Group | Interface Peel Strength (N / m) | Thermal Runaway Time (min) | Capacity Retention (%) | Example 1 | 22.3 | 102 | 98.6 | Example 2 | 22.0 | 99 | 96.2 | Example 3 | 22.1 | 100 | 97.1 | Example 4 | 23.1 | 84 | 76.3 | Example 5 | 18.9 | 89 | 85.2 | Example 6 | 24.7 | 76 | 86.9 | Example 7 | 23.5 | 81 | 87.4 | Example 8 | 16.4 | 80 | 87.5 | Example 9 | 15.8 | 73 | 85.7 | Comparative Example 1 | 18.4 | 20 | 97.9 | Comparative Example 2 | 19.6 | 75 | 89.8 | Comparative Example 3 | 19.7 | 62 | 85.2 | Comparative Example 4 | 21.6 | 65 | 84.3 | Comparative Example 5 | 17.2 | 57 | 82.5 | Comparative Example 6 | 21.9 | 74 | 80.1 | Comparative Example 7 | 22.2 | 70 | 95.4 | Comparative Example 8 | 20.3 | 78 | 74.6

[0093] Structural analysis:

[0094] Comparing the test performance of Examples 1-9 with that of Comparative Examples 1-8 in Table 1, it can be found that, compared with Comparative Examples 1-8, the composite negative electrode sheets provided by Examples 1-9 simultaneously possess higher interface peel strength, better electronic insulation effect, and higher ion transport efficiency, making the batteries using the composite negative electrode sheets less prone to internal short circuits, with better thermal stability and higher capacity cycle retention.

[0095] Comparing the electrodes and batteries provided in Example 1 with those in Comparative Examples 1-3, it can be found that the insulating coating on the composite negative electrode ensures normal lithium-ion transport during battery cycling and effectively prevents direct contact between the conductive components of the positive and negative electrodes. Even when the separator shrinks at high temperatures, it prevents internal circuitry in the battery. In Comparative Example 1, the battery lacks an insulating coating. Under high temperatures, the separator shrinks, leading to direct contact between the positive and negative electrodes, resulting in a shorter measured thermal runaway time. Comparative Example 2 provides an insulating coating on the separator surface. As shown in Table 2, Comparative Example 2 exhibits poor thermal stability and low capacity retention, with no significant improvement in lithium plating on the negative electrode. This is because the insulating coating adhering to the separator surface undergoes powdering, detachment, and folding under high temperatures as the separator shrinks, creating structural weaknesses that can lead to short circuits between the positive and negative electrodes. In the battery provided in Comparative Example 3, an insulating coating is provided on the surface of the positive electrode. However, material cross-contamination is likely to occur between the insulating coating and the active coating of the positive electrode, and there is no significant improvement effect on lithium plating on the negative electrode. As a result, the battery in Comparative Example 3 exhibits a shorter thermal runaway time and a lower capacity retention rate.

[0096] Comparing the performance indicators of the electrodes and batteries provided in Examples 1-3 with those in Comparative Examples 4-5 in Table 1, it can be found that the interfacial peel strength, thermal runaway time, and capacity retention rate measured in Examples 1-3 are all higher than those in Comparative Examples 4-5. This indicates that when the solubility parameter difference |Δδ| between the polymer and the binder is greater than 0.5, the composite negative electrode has higher structural stability and lower interfacial resistance between the insulating coating and the active coating. During the experiment, material cross-contamination was observed between the insulating coating and the active coating in the composite negative electrode provided in Comparative Examples 4-5, resulting in a decrease in battery cycle performance.

[0097] Comparing the electrodes and batteries provided in Example 1 with those in Comparative Examples 6-8, it can be found that the battery in Example 1 has higher thermal stability and cycle performance than the batteries provided in Comparative Examples 6-8. This indicates that when the insulating coating includes polymers, inorganic fillers, and fast ion conductors, the insulating coating has advantages such as electronic insulation and high ion transport efficiency, which can improve the overall performance of the battery. In Comparative Example 8, the interfacial impedance between the first and second coatings is relatively large, resulting in obstructed lithium-ion transport.

Claims

1. A composite negative electrode sheet, comprising a current collector, an active coating, and an insulating coating arranged sequentially, wherein the insulating coating comprises a polymer, an inorganic filler, and a fast ion conductor, and the active coating comprises a binder and an active material, wherein the solubility parameter difference between the polymer and the binder is expressed as |Δδ|, and |Δδ| > 0.5 (J / cm²). 3 ) 1 / 2 .

2. The composite negative electrode sheet as described in claim 1, wherein, In the insulating coating, the sum of the masses of the inorganic filler and the fast ion conductor is 80~94:6~20 of the mass of the polymer.

3. The composite negative electrode sheet as described in claim 1, wherein: The solubility parameter of the polymer is represented by δ1, which is 12.7~24.9 (J / cm³). 3 ) 1 / 2 ; The polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polypropylene, polyvinyl chloride, polyoxyethylene, polymethoxyethylene glycol methacrylate, polymethyl methacrylate, polyacrylonitrile, polycarbonate, polymethyl methacrylate, polyvinyl chloride, and polystyrene.

4. The composite negative electrode sheet as described in claim 1, wherein, The average particle size D50 of the inorganic filler is 20 nm to 3 μm, and the average particle size D50 of the fast ion conductor is 20 nm to 3 μm.

5. The composite negative electrode sheet as described in claim 4, wherein, The fast ion conductor includes at least one of lithium phosphate, lithium titanate, lithium titanium phosphate, lithium lanthanum tantalate, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum platinum, lithium lanthanum oxide, lithium superion conductor, and sodium superion conductor.

6. The composite negative electrode sheet as described in claim 4, wherein, The inorganic filler includes at least one of aluminum oxide, silicon dioxide, titanium dioxide, calcium oxide, zirconium oxide, diatomaceous earth, and kaolin.

7. The composite negative electrode sheet according to any one of claims 1 to 6, wherein, The porosity of the insulating coating is 30-80%.

8. The composite negative electrode sheet according to any one of claims 1 to 6, wherein, The thickness of the insulating coating is 0.5~50μm.

9. A method for preparing a composite negative electrode sheet as described in any one of claims 1 to 8, comprising the following operations: S1. Mix the binder and the active material evenly to obtain an active slurry, and apply the active slurry to the current collector to obtain the active coating; S2. The polymer and solvent are mixed evenly, and then the inorganic filler and the fast ion conductor are added to the reaction system to prepare an insulating slurry. The insulating slurry is applied to the active coating so that the insulating coating and the current collector are connected through the active coating to obtain the composite negative electrode sheet.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode comprises a composite negative electrode sheet as described in any one of claims 1 to 8.

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